Optical waveguide device and manufacturing method thereof

ABSTRACT

An optical waveguide device which is free from interference with an optical path between a light emitting element and an optical waveguide thereof, and to provide a method of manufacturing the optical waveguide device. A light emitting element ( 5 ) is provided on an upper surface of a first under-cladding layer ( 21 ), and a second under-cladding layer ( 22 ) is provided on the upper surface of the first under-cladding layer ( 21 ), covering the light emitting element ( 5 ). A core  3  which receives light emitted from the light emitting element ( 5 ) through the second under-cladding layer ( 22 ) is provided on an upper surface of the second under-cladding layer ( 22 ). The core ( 3 ) is located in a position such that the light emitted from the light emitting element ( 5 ) is incident on the core ( 3 ).

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/954,708, filed Aug. 8, 2007, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical waveguide device which iswidely used for optical communications, optical information processingand other general optics, and to a method of manufacturing the opticalwaveguide device.

2. Description of the Related Art

In general, optical waveguide devices are configured such that lightemitted from a light emitting element is transmitted through an opticalwaveguide (see, for example, U.S. Pat. No. 5,914,709). Such an opticalwaveguide device is schematically illustrated in FIG. 5. In FIG. 5, theoptical waveguide device includes an optical waveguide provided on asubstrate 10, and a light emitting element 50 fixed to the substrate 10by an adhesive A in spaced relation from one end of the opticalwaveguide. A light beam L from the light emitting element 50 is incidenton one end face of a core 30 of the optical waveguide, then transmittedthrough the core 30, and output from the other end face of the core 30.In FIG. 5, a reference numeral 20 denotes an under-cladding layer, and areference numeral 40 denotes an over-cladding layer.

In the optical waveguide device, however, the adhesive A is liable toprotrude to interfere with an optical path when the light emittingelement 50 is pressed from the above for bonding thereof.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide an optical waveguide device which is free from interference withan optical path between a light emitting element and an opticalwaveguide thereof, and to provide a method of manufacturing the opticalwaveguide device.

According to a first aspect of the present invention to achieve theaforementioned object, there is provided an optical waveguide device,which comprises: a light emitting element provided on an upper surfaceof a first under-cladding layer; a second under-cladding layer providedon the upper surface of the first under-cladding layer, covering thelight emitting element; and a core provided on an upper surface of thesecond under-cladding layer in a position such that light emitted fromthe light emitting element is incident on the core, the core beingadapted to receive the emitted light through the second under-claddinglayer.

According to a second aspect of the present invention, there is providedan optical waveguide device manufacturing method, which comprises thesteps of: placing a light emitting element on an upper surface of afirst under-cladding layer; forming a second under-cladding layer on theupper surface of the first under-cladding layer to cover the lightemitting element; and forming a core on an upper surface of the secondunder-cladding layer in a position such that light emitted from thelight emitting element is incident on the core, the core being adaptedto receive the emitted light through the second under-cladding layer.

The inventors of the present invention conducted studies on theconstruction of the optical waveguide device to eliminate theinterference with the optical path between the light emitting elementand the optical waveguide in the optical waveguide device. As a result,the inventors came up with an idea of burying and fixing the lightemitting element in an under-cladding underlying the core to allow thecore to receive light emitted from the light emitting element throughthe under-cladding, and further conducted experiments and studies.Consequently, the inventors attained the present invention, in which theaforementioned object is achieved based on this idea.

In the inventive optical waveguide device, the light emitting element isprovided on the upper surface of the first under-cladding layer, and thesecond under-cladding layer is provided on the upper surface of thefirst under-cladding layer, covering the light emitting element.Therefore, the light emitting element is buried and fixed in anunder-cladding configured as a laminate of the first under-claddinglayer and the second under-cladding layer. This obviates the use of anadhesive for the fixing of the light emitting element, or eliminates thepossibility of protrusion of the adhesive from the periphery of thelight emitting element if a very small amount of the adhesive is usedfor tentatively fixing the light emitting element on the upper surfaceof the first under-cladding layer prior to the formation of the secondunder-cladding layer. The inventive optical waveguide device ensuresproper light transmission between the light emitting element and thecore without the possibility that the adhesive interferes with theoptical path. Further, the light emitted from the light emitting elementis received on a bottom surface of the core through the secondunder-cladding layer, so that the core has a greater light receivingarea than in the conventional case in which the light is received by theone end face of the core. Thus, the light transmission is more reliablyachieved.

Particularly, one end portion of the core serves as a light receivingportion for receiving the light emitted from the light emitting element,and an end surface of the light receiving portion is inclined at anangle of 45 degrees with respect to the bottom surface of the core.Further, the light emitted from the light emitting element is projectedat an angle of 45 degrees with respect to the inclined surface. In thiscase, the light emitted from the light emitting element is reflected onthe inclined surface, whereby the optical path is efficiently deflectedto extend longitudinally of the core. Thus, the light transmissionefficiency is improved.

In the inventive optical waveguide device manufacturing method, thelight emitting element is placed on the upper surface of the firstunder-cladding layer, and then the second under-cladding layer is formedon the upper surface of the first under-cladding layer to cover thelight emitting element. Thereafter, the core which receives the lightemitted from the light emitting element through the secondunder-cladding layer is formed on the upper surface of the secondunder-cladding layer in the position such that the light emitted fromthe light emitting element is incident on the core. Therefore, theinventive optical waveguide device can be provided, which ensures properand highly reliable light transmission.

A light-receiving end surface of the core is formed inclined at an angleof 45 degrees with respect to the bottom surface of the core, andpositioned so that the light emitted from the light emitting element isprojected at an angle of 45 degrees with respect to the inclinedsurface. In this case, the light emitted from the light emitting elementis reflected on the inclined surface, whereby the optical path isefficiently deflected to extend longitudinally of the core. Thus, theoptical waveguide device is improved in light transmission efficiency.

Where one end portion of the core is cut by moving a blade having anedge angle of 90 degrees along a light projection axis of the lightemitting element for the formation of the inclined light-receiving endsurface of the core, the blade can be easily positioned. This makes itpossible to accurately and easily position the inclined surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically illustrating an opticalwaveguide device according to one embodiment of the present invention.

FIGS. 2( a) to 2(f) are explanatory diagrams schematically showing anoptical waveguide device production method according to the presentinvention.

FIG. 3 is an explanatory diagram schematically illustrating amodification of the optical waveguide device production method.

FIG. 4 is an explanatory diagram schematically illustrating amodification of the optical waveguide device.

FIG. 5 is a sectional view schematically illustrating a conventionaloptical waveguide device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described indetail with reference to the attached drawings.

FIG. 1 illustrates an optical waveguide device according to oneembodiment of the present invention. In this embodiment, the opticalwaveguide device is provided on an upper surface of a substrate 1. Inthe optical waveguide device, a light emitting element 5 is buried andfixed in an under-cladding 2 including a first under-cladding layer(lower layer) 21 and a transparent second under-cladding layer (upperlayer) 22 stacked one on the other, and a core 3 serving as a path of alight beam L is provided in a predetermined pattern on an upper surfaceof the second under-cladding layer 22. In this embodiment, anover-cladding layer 4 is provided which covers the core 3. The lightemitting element 5 is adapted to project the light beam L verticallyupward, and one end portion of the core 3 serving as a light receivingportion is positioned just above the light emitting element 5. An endsurface 3 a of the light receiving portion is inclined at an angle of 45degrees with respect to a bottom surface of the core 3. In FIG. 1, areference character 5 a denotes a lead frame having one end portion onwhich the light emitting element 5 is fixed, and the other end portionprovided with terminals (wiring connection portions) 5 b connected tothe light emitting element 5. Further, a reference character H denotes acut hole which is formed by means of a rotary blade D (see FIG. 2( f))for forming the inclined surface 3 a on the light receiving portion.

The light beam L projected vertically upward from the light emittingelement 5 passes through the second under-cladding layer 22, and isincident on a bottom surface of the one end portion of the core 3 toenter the core 3. Then, the light beam L is reflected on the inclinedsurface 3 a at an angle of 45 degrees, whereby an optical path isdeflected to extend longitudinally of the core 3. Then, the light beam Ltravels along the length of the core 3, and is output from the other endsurface of the core 3.

An exemplary production method for the optical waveguide device will bedescribed.

First, a planar substrate 1 (see FIG. 2( a)) is prepared. The substrate1 is not particularly limited, but exemplary materials for the substrate1 include glass, quartz, silicon, resins and metals. The thickness ofthe substrate 1 is not particularly limited, but is typically in therange of 20 μm to 5 mm.

In turn, a first under-cladding layer 21 is formed in a predeterminedregion of an upper surface of the substrate 1 as shown in FIG. 2( a).Examples of a material for the formation of the first under-claddinglayer 21 include photosensitive resins, polyimide resins and epoxyresins. The formation of the first under-cladding layer 21 is achievedin the following manner. A varnish prepared by dissolving any of theaforementioned resins in a solvent is applied on the substrate 1. Theapplication of the varnish is achieved, for example, by a spin coatingmethod, a dipping method, a casting method, an injection method, an inkjet method or the like. Then, the varnish is cured. Where aphotosensitive resin is employed as the material for the formation ofthe first under-cladding layer 21, the curing is achieved by exposingthe applied varnish to radiation. An exposed portion of the varnishserves as the first under-cladding layer 21. Where a polyimide resin isemployed as the material for the formation of the first under-claddinglayer 21, the curing is typically achieved by a heat treatment at 300°C. to 400° C. for 60 to 180 minutes. The thickness of the firstunder-cladding layer 21 is typically in the range of 5 to 50 μm. Thus,the first under-cladding layer 21 is formed.

Next, a light emitting element 5 is placed together with a lead frame 5a in a predetermined position on an upper surface of the firstunder-cladding layer 21 as shown in FIG. 2( b). At this time, terminals(wiring connection portions) 5 b provided on the other end portion ofthe lead frame 5 a are positioned outward of an edge of the firstunder-cladding layer 21. The placement of the light emitting element 5may be achieved with the use of no adhesive or with the use of a verysmall amount of an adhesive for tentative fixing thereof. This isbecause the light emitting element 5 is fixed in the subsequent step(see FIG. 2( c)), in which a transparent second under-cladding layer 22is formed on the upper surface of the first under-cladding layer 21 inthe same manner as in the formation of the first under-cladding layer 21to cover the light emitting element 5. Examples of a material for theformation of the second under-cladding layer 22 include those employedas the material for the formation of the first under-cladding layer 21,but a transparent one is selected from those materials. Typicallyemployed as the light emitting element 5 is a light emitting diode, alaser diode, a VCSEL (Vertical Cavity Surface Emitting Laser) or thelike.

Thus, the light emitting element 5 is buried and fixed in anunder-cladding 2 configured as a laminate of the first under-claddinglayer 21 and the second under-cladding layer 22 as shown in FIG. 2( c).In this state, the terminals (wiring connection portions) 5 b of thelight emitting element 5 are exposed out of an end face of theunder-cladding 2.

Subsequently, a core 3 is formed on an upper surface of the secondunder-cladding layer 22 as shown in FIG. 2( d). At this time, one endportion of the core 3 is positioned just above the light emittingelement 5. A material for the formation of the core 3 is typically aphotosensitive resin, which has a greater refractive index than thematerial for the formation of the second under-cladding layer 22 and amaterial for formation of an over-cladding layer 4 (see FIG. 2( e)) tobe described later. The refractive index may be adjusted, for example,by selection of the types of the materials for the formation of thesecond under-cladding layer 22, the core 3 and the over-cladding layer 4and adjustment of the composition ratio thereof. The formation of thecore 3 is achieved in the following manner. A varnish prepared bydissolving the photosensitive resin in a solvent is applied on theunder-cladding layer 22 in the same manner as described above. Theapplication of the varnish is achieved in the same manner as describedabove, for example, by a spin coating method, a dipping method, acasting method, an injection method, an ink jet method or the like.Then, the varnish is dried to form a resin layer. The drying istypically achieved by a heat treatment at 50° C. to 120° C. for 10 to 30minutes.

Then, the resin layer is exposed to radiation through a photo mask (notshown) formed with an opening pattern corresponding to a pattern of thecore 3. An exposed portion of the resin layer serves as the core 3 afteran unexposed portion removing step. More specifically, examples of theradiation for the exposure include visible light, ultraviolet radiation,infrared radiation, X-rays, α-rays, β-rays and γ-rays. Preferably, theultraviolet radiation is used. The use of the ultraviolet radiationpermits irradiation at a higher energy to provide a higher curing speed.In addition, a less expensive smaller-size irradiation apparatus can beemployed, thereby reducing production costs. Examples of a light sourcefor the ultraviolet radiation include a low-pressure mercury-vapor lamp,a high-pressure mercury-vapor lamp and an ultra-high-pressuremercury-vapor lamp. The dose of the ultraviolet radiation is typically10 to 10000 mJ/cm², preferably 50 to 3000 mJ/cm².

After the exposure, a heat treatment is performed to complete aphotoreaction. The heat treatment is performed at 80° C. to 250° C.,preferably at 100° C. to 200° C., for 10 seconds to two hours,preferably for five minutes to one hour. Thereafter, a developmentprocess is performed by using a developing agent to dissolve away anunexposed portion of the resin layer. Thus, the remaining portion of theresin layer has the pattern of the core 3. Exemplary methods for thedevelopment include an immersion method, a spray method and a puddlemethod. Examples of the developing agent include an organic solvent andan organic solvent containing an alkaline aqueous solution. Thedeveloping agent and conditions for the development are properlyselected depending on the composition of the photosensitive resin.

Then, the developing agent in the remaining resin layer having thepattern of the core 3 is removed by a heat treatment. The heat treatmentis typically performed at 80° C. to 120° C. for 10 to 30 minutes. Theremaining resin layer thus patterned serves as the core 3. The core 3typically has a thickness of 5 to 30 μm, and typically has a width of 5to 30 μm.

Then, as shown in FIG. 2( e), an over-cladding layer 4 is formed on theupper surface of the second under-cladding layer 22 to cover the core 3.Examples of a material for the formation of the over-cladding layer 4include those employed as the materials for the first and secondunder-cladding layers 21, 22. The material for the formation of theover-cladding layer 4 may be the same as or different from the materialsfor the formation of the first and second under-cladding layers 21, 22.The formation of the over-cladding layer 4 is achieved in the samemanner as the formation of the first or second under-cladding layer 21,22. The thickness of the over-cladding layer 4 is typically 20 to 100μm.

Further, the terminals (wiring connection portions) 5 b of the lightemitting element 5 are respectively connected to wirings 6 by a wirebonding method or the like.

Then, the one end portion of the core 3 is cut by moving a disk-shapedrotary blade D having an edge angle of 90 degrees downward toward thebottom surface of the core 3 from above the over-cladding layer 4 whilerotating the rotary blade D. Thus, the core 3 has a surface 3 a inclinedat an angle of 45 degrees with respect to the bottom surface of the core3.

Thus, the optical waveguide device (see FIG. 1) including theunder-cladding 2 having the light emitting element 5 buried therein, thecore 3 and the over-cladding layer 4 is produced on the upper surface ofthe substrate 1.

In the embodiment described above, when the one end portion of the core3 is cut, the light beam L is projected vertically upward from the lightemitting element 5 as shown in FIG. 3. At this time, the projected lightmay be employed as a reference, and the rotary blade D may be moved downin an arrow direction X along a light projection axis (with a rotatingsurface of the rotary blade D being oriented along the light projectionaxis) for the cutting. For the cutting, the rotary blade D is positionedso that a generally middle portion of the inclined surface 3 a to beformed intersects the light projection axis (in FIG. 3, a widthwisecenter of the rotary blade D is illustrated as being offset to the leftside from the light projection axis). By employing the light projectionas the reference, the positioning of the rotary blade D for the cuttingis facilitated, so that the inclined surface 3 a can be more accuratelyand easily positioned.

In the embodiment described above, the light beam is projectedvertically upward from the light emitting element 5, and the end surface3 a of the core 3 inclined at an angle of 45 degrees is positioned justabove the light emitting element 5. However, this arrangement is notlimitative. For example, the light beam may be projected obliquelyupward from the light emitting element 5, and a portion (light receivingportion) of the core 3 may be positioned with respect to the lightprojection axis in an optical waveguide device as shown in FIG. 4. Thatis, an intermediate portion (light receiving portion) of the core 3 ispositioned obliquely upward of the light emitting element 5 with respectto the light projection axis in the optical waveguide device shown inFIG. 4. In this optical waveguide device, the light beam L is incidenton the portion (light receiving portion) of the core 3, and travelslongitudinally in the core 3 while being repeatedly reflected in thecore 3. In this case, there is no need to form the inclined surface 3 a(see FIG. 1) on the one end portion of the core 3.

The over-cladding layer 4 is provided in the embodiments described above(see FIGS. 1 and 4), but the over-cladding layer 4 is not essential. Theoptical waveguide device may be configured without the provision of theover-cladding layer 4.

Next, an inventive example will be described. However, the presentinvention is not limited to the example.

EXAMPLE Material for Formation of First and Second Under-Cladding Layersand Over-Cladding Layer

A material for formation of first and second under-cladding layers andan over-cladding layer was prepared by mixing 35 parts by weight ofbisphenoxyethanolfluorene diglycidyl ether (Component A), 40 parts byweight of 3′,4′-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylatewhich is an alicyclic epoxy resin (CELLOXIDE 2021P manufactured byDaicel Chemical Industries, Ltd.)(Component B), 25 parts by weight of(3′,4′-epoxycyclohexane)methyl-3′,4′-epoxycyclohexyl-carboxylate(CELLOXIDE 2081P manufactured by Daicel Chemical Industries, Ltd.)(Component C), and 1 part by weight of a 50% propione carbonate solutionof 4,4′-bis[di(β-hydroxyethoxy)phenylsulfinio]phenylsulfidebishexafluoroantimonate (photoacid generator, Component D).

Material for Formation of Core

A material for formation of a core was prepared by dissolving 70 partsby weight of the aforementioned component A, 30 parts by weight of1,3,3-tris{4-[2-(3-oxetanyl)]butoxyphenyl}butane and 0.5 part by weightof the aforementioned component D in 28 parts by weight of ethyllactate.

Production of Optical Waveguide Device

The first under-cladding layer material was applied on an upper surfaceof a glass substrate (having a thickness of 1.0 mm) by a spin coatingmethod, and then irradiated with ultraviolet radiation at 2000 mJ/cm².Subsequently, a heat treatment was performed at 100° C. for 15 minutes,whereby a first under-cladding layer (having a thickness of 15 μm) wasformed.

Next, a light emitting diode was tentatively fixed to an upper surfaceof the first under-cladding layer with the use of a very small amount ofa UV-curable adhesive.

Then, a second under-cladding layer (having a thickness of 10 μm) wasformed on the upper surface of the first under-cladding layer in thesame manner as in the formation of the first under-cladding layer tocover the light emitting diode.

Subsequently, the core material was applied on an upper surface of thesecond under-cladding layer by a spin coating method, and dried at 100°C. for 15 minutes. In turn, a synthetic quartz photo mask having anopening pattern conformable to a core pattern was placed above theresulting core material film. After the core material film was exposedto ultraviolet radiation emitted from above at 4000 mJ/cm² by a contactexposure method, a heat treatment was performed at 120° C. for 15minutes. Subsequently, a development process was performed by using aγ-butyrolactone aqueous solution to dissolve away an unexposed portion,and then a heat treatment was performed at 120° C. for 30 minutes,whereby a core (having a sectional size of 12 μm (width)×24 μm (height))was formed.

In turn, the over-cladding layer material was applied on the secondunder-cladding layer to cover the core by a spin coating method, andthen irradiated with ultraviolet radiation at 2000 mJ/cm². Subsequently,a heat treatment was performed at 150° C. for 60 minutes. Thus, anover-cladding layer (having a thickness of 35 μm) was formed.

Then, wirings were respectively connected to terminals of the lightemitting diode by a wire bonding method.

Subsequently, light was projected vertically upward from the lightemitting diode and, in this state, a rotary blade having an edge angleof 90 degrees was moved down from above the over-cladding layer along alight projection axis by means of a dicing machine (Model 522 availablefrom Disco Corporation) to cut one end portion of the core at an angleof 45 degrees with respect to a bottom surface of the core to form aninclined surface on the one end portion.

Thus, an optical waveguide device including the under-cladding havingthe light emitting diode buried therein, the core and the over-claddinglayer was produced on the substrate.

Although a specific form of embodiment of the instant invention has beendescribed above and illustrated in the accompanying drawings in order tobe more clearly understood, the above description is made by way ofexample and not as a limitation to the scope of the instant invention.It is contemplated that various modifications apparent to one ofordinary skill in the art could be made without departing from the scopeof the invention which is to be determined by the following claims.

1. An optical waveguide device comprising: a first under-cladding layer;a light emitting element provided on an upper surface of the firstunder-cladding layer; a second under-cladding layer provided on theupper surface of the first under-cladding layer, covering the lightemitting element; and a core provided on an upper surface of the secondunder-cladding layer in a position such that light emitted from thelight emitting element is incident on the core, the core being adaptedto receive the emitted light through the second under-cladding layer. 2.An optical waveguide device as set forth in claim 1, wherein one endportion of the core serves as a light receiving portion for receivingthe light emitted from the light emitting element, and an end surface ofthe light receiving portion is inclined at an angle of 45 degrees withrespect to a bottom surface of the core, wherein the light emitted fromthe light emitting element is projected at an angle of 45 degrees withrespect to the inclined surface.
 3. An optical waveguide devicemanufacturing method comprising the steps of: forming a firstunder-cladding layer; placing a light emitting element on an uppersurface of the first under-cladding layer; forming a secondunder-cladding layer on the upper surface of the first under-claddinglayer to cover the light emitting element; and forming a core on anupper surface of the second under-cladding layer in a position such thatlight emitted from the light emitting element is incident on the core,the core being adapted to receive the emitted light through the secondunder-cladding layer.
 4. An optical waveguide device manufacturingmethod as set forth in claim 3, wherein a light-receiving end surface ofthe core is formed inclined at an angle of 45 degrees with respect to abottom surface of the core and positioned so that the light emitted fromthe light emitting element is projected at an angle of 45 degrees withrespect to the inclined surface.
 5. An optical waveguide devicemanufacturing method as set forth in claim 4, wherein one end portion ofthe core is cut by moving a blade having an edge angle of 90 degreesalong a light projection axis of the light emitting element forformation of the inclined light-receiving end surface of the core.